Photolithography



Nov. 24, 1 970 WANSM/Tm/VCE z. GILFERT 3,543,291

do f

WAVE LENGTH '//V M/LL/M/(POA/S' INVENTOR. JACK z. G/L FEET POM l m;/(/V0.8BE a Mnleravs United States Patent 3,543,291 PHOTOLITHOGRAPHYJack Z. Gilfert, Carmichael, Califi, assignor to Bolls & King, a limitedpartnership Filed Feb. 17, 1967, Ser. No. 616,970 Int. Cl. G03f 7/02 US.Cl. 96-33 10 Claims ABSTRACT OF THE DISCLOSURE A planographic, singleemulsion, monochromatic, fine silver halide grain, high contrast,non-ultraviolet transmitting photographic film for use when colordeveloped and fixed in exposing ultraviolet sensitive photomechanicalreproduction plates, and a method of preparing such films by colorcoupler development of azomethine dyes in silver salt grain gelatinemulsions.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to photographic films and to methods of preparing and using highcontrast, graphic arts, photographic films in the preparation of platesfor photomechanical reproduction.

DESCRIPTION OF THE PRIOR ART In lithographic and gravure processes ofprinting, an exposed and developed photographic film is utilized toprepare a printing surface to receive ink that is mechanicallytransferred directly or indirectly to a paper surface.

Printing plates are composed of a base material which may be metal suchas aluminum or zinc, or paper or other supports, depending upon thefinal use, and contain coatings which are sensitive to light mainly inthe ultraviolet (300 to 400 m and somewhat in the blue visible (400 to500 mg) ranges of the spectrum. Typical coatings are bichromated albuminor gum arabic or diazo-sensitized coatings such as a water soluble resinformed by the reaction of diazo-diphenylamine and formaldehyde. Whenthese plates are exposed to a lamp which emits a substantial amount ofultraviolet light such as an arc lamp, the exposed portions areactivated and can then be hardened by development.

Portions of the surface of the printing plate when properly treatedeither absorb greasy inks or repel them and the plate has no ability todistinguish or print gradation of tone. The ink goes down on the paperfollowing the same all-or-nothing principle. Therefore, reproduction islimited to copy having no intermediate tones. In line copy, lines,spots, type and other high density deposits form images by contrastbetween the paper and the printed copy. A uniform amount of ink isdeposited on the paper by the printing surface wherever the plate bearsan image, and the paper remains'clear wherever there is no image.

This same principle is adapted to produce images appearing to have tonalgradations from white to black. Continuous tone copy having intermediatetones of gray can be photographically transformed into a series of dotsin which the dot pattern creates the impression of an intermediate tone.Each dot is not discernible to the naked eye and is surrounded by aclear area. When the image is printed, the dots and white paper betweenthe dots fuse visually and the eye sees intermediate tones. These dotsaccept ink according to the same all-or-nothing principle. Thus, thecameraman can break up a continuous tone original into a half-toneinterpretation that can be printed.

Many special effects can be obtained. In the tone-line process aregistered negative and a positive of nearly equal contrast of acontinuous tone image are combined with the positive as a mask and aprint is made on a high contrast film. A line positive is produced whichsimulates a pen-and-ink drawing. Shadow and detail such as stippling orhand painted dots can be added to the positive.

In printing, a copy is translated to a form which will permit the pressto reproduce the original as closely as possible. In the translation ofthe original copy to its final printed form, numerous intermediate stepsare necessary, each contributing to the progress of the work. The fivesteps are generally (1) camera work, (2) art work, (3) stripping, (4)plate making, and (5) press work.

The camera work depends on the copy received. It can be single colorcopy or multi-color copy and these may be subdivided into line or halftone. When there is a definite black and white or its equivalent ofsolid contrasting elements making up a copy similar to that found intype, lettering or any other copy that is produced in full strength inkstrokes of whatever ink, that copy is said to be line work, whether ornot it contains half tone dots. Any copy that can be reproduced withoutthe aid of a half tone screen, can be called line copy.

Each surface that makes up the image, whether minute or large, Whetherpinpoint dot or solid area, carries the same strength of ink. Theillusion of the various tones present in a regular continuous tonephotograph, is accomplished by breaking up the image into dots ofvarying size but of equal true density. The size of a particular dotdepends among other things upon two main factors: (1) amount of lightreflected from the copy, and (2) the kind of screen used between thelight source and the photographic plate or film. The ratio of the dotsize to the white surrounding it determines the value of the apparenttone. The equal true density is effected by use of high contrast filmthat is processed to an even density of gray in all exposed areas.

There are many types of screens such as circular, irregular design,lenticular and grain. The most widely used, however, is the half tonescreen consisting of a series of parallel opaque lines. The lines areusually exactly as wide as the spaces between them and come in series of60 lines to 300 or more lines per inch. As the dots become more numerousand the spaces between them smaller, it becomes harder to print becausethe white portions are harder to keep on the press. Consequently, and133 lines screen are most popular in lithography. They give the bestrendition with the least trouble.

To obtain the dot formation in the negative or positive, the half tonescreen can be introduced in the camera while making the exposure or inthe vacuum frame while making a contact. In the camera the screen isplaced just before and parallel to the light sensitive emulsion andbetween it and the lens. In the vacuum frame process the screen or acopy of it is placed between the continuous tone negative or positiveand the photolithographical emulsion, with emulsion side of the screencopy down.

During exposure a reversal takes place in that the light rays alfect thesensitive emulsion in the clear areas of the 3 negative. This forms alatent image made visible by development. The portions unaffected bylight dissolve away in the fixing process. These clear sections actuallyrepresent the work or image.

Color reproduction is made possible due to the ability of a plurality ofsuperimposed monochromes to reproduce all colors. In the commonly usedmethods of color printing, color separation negatives are made by use offilters or mask and these are converted to half-tones which the presscan print. It is possible to form the separation half-tone directly by astep known as direct screening.

The preparation of a printing plate from a single negative or positivefilm is a simple procedure which can be either by direct contact orprojection exposure. However, when a plurality of films are layed outadjacent one another, such as different lined screened half-tones orsuperimposed such as during surprinting of detail or lettering or incolor separation printing, it is extremely difiicult to assure perfectregister of the dot patterns.

High contrast photographic film is transparent in the printing areas andcontains opaque black silver in the nonprinting areas. The completeopacity of the latter areas and the inability to see through the dotareas on the layout table even with illumination has added substantialcomplexity and risks of error to layout procedures. In the case of colorwork where exact registration is essential in order to avoid blurred dotpatterns or the moire effect, it has been found necessary to place colorregistration marks on the original art work which are reproduced on eachof the color separation negatives and on the corresponding half-tones.Even so, if the registration marks have any breadth to them at all, theregistration of the half-tones can be olf and the final printing platesburned from these half-tones would not produce a satisfactory print.Furthermore, in stripping a half-tone film to a line film in properposition, a considerably larger cutout has to be made in the line film,before the half-tone is entered and taped into position. The half-tonecan easily shift position again ruining the final printing plate that isprepared from this layout.

SUMMARY OF THE INVENTION In accordance with the invention, thelimitations of working with a film having opaque areas are substantiallyeliminated and the modified film of the invention, produced in anefiicient and controllable manner, allows much more flexibility inpreparing plates for photomechanical reproduction. The opaque blacksilver nonprinting area, i.e. the completely opaque areas and thehalftone dot areas of the high contrast film, are converted according tothe invention into dyed transparent areas of a pronounced color which donot allow transmission of any significant amounts of the ultraviolet andblue wavelength light that exposes and initiates the hardening of thesensitive coatings of photon-rechanical reproduction plates. As comparedto the irregular and fuzzy silver opaque areas, the corresponding dyedareas of the invention allow at least as good resolution since the dyemolecules are more finite and give a more definite record facilitatingalignment of the now pronounced colored dot patterns.

Perfect register in any close register work whether in abutting relationor in superposed relation, becomes much simplified since the operatorcan now see through the formerly opaque areas and with the aid ofmagnification can adjust the relationship of the films to the exactdesired position. This is all done much more efiiciently and easily thanwith the former black images. Then by the use of a punch, mating holesare placed in all negatives in at least two positions and accurateregistration on the plate is guaranteed by use of these mechanicalregistering means during exposure.

In the stripping of one film to another, the transparent high contrastfilm can be placed in its correct position on the line work initially,and the cutout can then be made to exact measurements eliminatingshifting or other changes and allowing for a smaller cutout. Even in thelayout of a single film to a masking sheet, the operation is muchsimplified since the operator can at all times view exactly what isbeing done since more light passes through the film to the masking sheetallowing easier viewrng.

With a transparent high contrast film, a design can be repeated on aplate by a step-off repeat process much more accurately than beforesince registration marks on the plate will be visible through the filmand allow exact and speedy placement to be effected without expensivespecial equipment formerly required. Forgotten or correction detail orforgotten half-tones can be added to an exposed or finished plate thatformerly would have to be discarded. The exposed and developedsensitized coating can be honed ofi in the error area and resensitizedby means of a wipe-on sensitizing liquid, and then the transparent highcontrast film can be visually placed in exact position on the plate andthe plate exposed and developed in the usual manner, thus saving anotherwise useless plate.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a series of graphs showingthe percentage transmission of radiation as the ordinate versus theradiation wavelength as the abcissa for a typical yellow dye, magentadye, and a combination of yellow and magenta dyes.

FIG. 2 is a vertical section of a film which forms part of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preparation of the colored,transparent, high contrast film according to the invention, makes use ofmaterials and processing techniques familiar to the printing industry.The films are produced by photochemical processing of high contrastgraphic arts photographic films. These films are special materialstypically reserved for making line or screen negatives or positives.Line or litho-film is clearly distinguishable from continuous-tone filmin several particulars. Litho-film has a steep low-to-high densitycharacteristic sensitometric curve (i.e. density versus exposure) whichis responsible for the clear black and white definition between line andhalf-tone dots versus clear background. These films are described, forexample, on page 12 of Films and Plates for the Graphic Arts, KodakGraphic Arts Data Book Q-2, Eastman Kodak Company, 4th Edition, 1961:

The angular slope of such almost vertical line-film sensitometric curvesis of the order of about 75-85 degrees, more or less, on graphs plottingdensity units (ordinate) as a function of the logarithm of exposure(abcissa), with the units of density and exposure having the same scale.Typical curves of this character are presented, for example, on datasheet D4 of the said book.

Continuous-tone film, on the other hand (page 10 of the said Data Book),generally has an angular slope in its sensitometric curve that is muchless steep, of the order of about 30 to 45 degrees, more or less, in theinitial portion thereof. Reference may be made, for example, to datapage D-19 of the said book. Other well-known characteristic differencebetween line and continuous-tone film are the following:

Line film: Continuous-tone film: Generally orthochromat- Generallypanchromatic ic.

Maximumgamma generally about 1 to 2. Maximum density generally about 1.5to 2.

High-speed emulsion.

The sharp cutoff high contrast charcteristics are provided in thesefilms by the nature of the silver halide grains. The grains in a highcontrast film are very small, typically averaging less than 0.3 micronand usually averaging about 0.1 micron in a very small sizedistribution. The silver halide grains in continuous tone films are muchlarger, of the order of an average of 3 to 5 microns, and aredistributed over a large size range. The smaller grain emulsions areslower speed and are not sensitive to low intensity light. Theseemulsions are developed with energetic developers. An importantcharacteristic being that the high contrast films develop to an image ofeven tonal density. That is, each dot or line will be of even blacknessor density and will absorb light equally. There is an absence of tonalgradation in the final exposed and developed film.

Several present day commercial examples of line film are those soldunder the trademark Kodalith Ortho- Ester Base (Eastman Kodakdata pagesD-9 through 9-17 of the said book); under the trade name Reprolith(Ansco); under the mark Photolith (Du Font); and under the name ProcessExtra Ortho (Gevaert).

The plate developing wavelengths that should not be transmittedsubstantially are those from just below visible to slightly abovevisible from about less than 500 millimicrons to about 300 millimicronswith more extreme sensitivity in the range of 350450 millimicrons. Onexposure of the sensitized plate to ultraviolet light, only the filmareas absent opaque silver transmit this light and are hardened byphotochemical action. The black opaque areas prevent the transmission oflight by absorption. The present invention is based on providingmaterials that prevent transmission of light capable of activatingdevelopment of presensitized printing plates but yet allow transmissionof the remaining visible light.

According to the invention, the reduced black silver in metal form isconverted to organic stable dyes having the characteristic of preventingtransmission of light that would expose the plate.

By reference to FIG. 1 which is a series of graphs of the percentagetransmission of radiation as ordinate versus radiation wavelength asabscissa for a typical yellow and magenta dye and their combination, itcan be seen from Curve A, which relates to the transmission of a typicalyellow organic dye, that this dye substantially prevents transmission ofmore than 10 per cent of the short wavelength ultraviolet and blue lightof concern. Curve B illustrates the transmission characteristics of amagenta dye, and Curve C is a combined characteristic of the two whichwould in essence be an orange-red to red dye. This is in reality ofsubtractive method of color mixing and Curves A and B represent thetransmission curves of a yellow and magenta filter respectively. Whenthese two filters are inserted in a beam of white light from aprojection lantern, a fraction of the incident light is absorbed orreflected as the light passes through the first filter and the remaininglight then passes through the second filter where this fraction is againfiltered and the fraction of the fraction is what is transmitted. Thus,at 500 m percent of the incident light is transmitted by the yellowfilter, and 11 percent of this fraction is transmitted by the magentafilter. Hence, Curve C, the transmittance of the combination, is foundby multiplying the transmittance curves of the filters together at eachwavelength. The final result is the same whether the filters are inadjacent relationship or color bodies which act as the filters areintimately mixed in a transparent support such as the photographicemulsion of the present invention.

The suspended particles of dye behave like tiny filters in the path ofthe light rays entering the support or vehicle. Since the light rayspass through both yellow and magenta filters before being reflected fromthe top surface or penetrating and leaving the bottom surface, theeffect is the same as that produced when the yellow and magenta filtersare placed in series in the path of a light beam. Nonprinting areas ofthe plate are not exposed and hardened if less than 20 percent of theprojected radiation in the 300 to 500 m range is transmitted, andpreferably less than 10 percent of this radiation is transmitted in the350 to 450 m range.

The yellow dye alone sufiiciently inhibits transmission of substantialultraviolet and blue light. However, by reference to Curve C, it isapparent that the combined characteristics of the two dyes are much moreetfective in transmitting less light in the desired range and theredorange dot patterns are much more pronounced and evident against aclear background as compared to the corresponding yellow dot patterns.However, substantial light above 500 millimicrons is still transmittedso that dots and lines of distinct color are still sufficiently transparent to allow superimposed viewing during alignment and registration.

The conversion of the silver image whether in latent or exposed form isaccomplished according to the invention by dye coupling colordevelopment of silver salts. Certain difunctional aromatic amines whenpresent during the development of silver will couple with the reducedsilver to simultaneously form an insoluble dye image which remains whenthe silver is removed from the emulsion to leave a transparent dyedarea. As the production of dye is directly connected with the reductionof silver, the dye will form a positive image, the intensity of which isrelated to the concentration of reduced silver.

There are two basic types of coupling developers, derivatives ofp-phenylenediamine and derivatives of paminophenol both coupling at theamino group so that the amino group in the aminophenol developers andone of the amino groups in the p-phenylenediamine developers must beunsubstituted.

There are also two general types of couplers, hydroxyaromatics such asphenols or naphthols and materials containing an active methylene group(O=CCH C=O). A phenylenediamine couples with the phenol to form anindoaniline dye, a p-aminophenol derivative couples with the phenol toform an indophenol dye and the dyes formed when either developer coupleswith an active methylene group are called azomethine dyes. The phenol ornaphthol couplers form dyes which generally absorb light in the red endof the spectrum, thus reflecting and transmitting cyan or bluewavelength lights, the opposite of the intended eflect of the invention.Couplers which are pyrazolones, cyanoacetyl compounds and derivatives ofp-nitrobenzylcyanide when coupled with diethyl-p-phenylenediamine formdyes with the major absorption of radiant energy in the green region ofthe spectrum, thus leading to magenta or orange dyes. A few of thebetter known couplers are shown in the following table.

TABLE I 1-p-nitrophenyl-3-methyl-5-pyrazolone1-phenyl-3-methyl-5-pyrazolone p-Nitrobenzylcyanide BenzoylacetonitrileNapthoylacetonitrile Couplers with the active methylene group betweentwo C=O groups give dyes mainly absorbing blue wavelength light and thusare yellow or orange. A few of the better known couplers are shown inthe following table.

TABLE II Ethylacetoacetate Ethyl benzoylacetate Acetoacetanilidep-Napthoylacetone Diethyl malonate Thus, the yellow, orange or magentadyes are of the azomethine type.

The p-aminophenols developers and the substituted dcrivatives thereofhave not been used much in practice because of solubility andinstability the dyes formed from these developers. The most importantdevelopers used for coupling are the substituted p-phenylenediamines.These may have one or both of the hydrogen atoms on one of the nitrogenssubstituted by lower alkyl, aryl or substituted lower alkyl such as thegroups:

where R is alkylene or arylene, R is hydrogen or lower alkyl and n is1-5. The benzene ring may also carry similar substituents such as loweralkyl. Typical p-phenylenediamine derivatives useful as the colordevelopers of this invention are p-toluenediamine,di-methyl-p-phenylenediamine, diethyl-p-phenylenediamine and 2-amino-5-diethylaminotoluene. These developers are sometimes marketed as an acidaddition salt such as the hydrochloride.

The invention may be practiced with the silver salts of the emulsion inan exposed latent image form or in an exposed and developed form. In thelatter case, it is required that the silver be returned to a salt whichis reduceable by color developing reducing agents. The color developingagents may be in a processing solution or may form a part of thephotographic emulsion.

In the instance where the silver is in a reduced, developed form, thematerial to be processed is a previously exposed high contrast materialdiscussed above, such as a half-tone or line film made by any of themultitude of graphic art processes whether of the one, two, three orfour multiple step procedures for preparing a line or half-tone image ina high contrast film in a form suitable for exposure of a presensitizedprinting plate. For example, a line positive can be made on a suitablecommercial film such as Kodalith Orthofilm Type 3, according to theprocedure set forth in the pamphlet entitled Kodak Tone-Line Process,Kodak Pamphlet No. Ql8 (1963), or a half-tone can be made on the samefilm according to the procedure disclosed in Kodak Publication Q1entitled Basic Photography for the Graphic Arts. The film could be madewith many of the other materials available on the market, and it couldalso be made with self-masking or autoscreen type of films. The mannerof exposing and developing the high contrast film follows proceduresWellknown in the art, that are not important to the invention exceptthat recommended procedures should be observed in order to prepare ahigh quality, high contrast developed film of good rendition andresolution. The black and white high contrast developer can be any ofthe high energy solutions normally utilized, such as hydroquinone,hydroquinone-paraformaldehyde, hydroquinone-metol or the metol type.

In order to practice the rebleach process, the silver in metallic formmust be converted to a reducible salt form. The silver salt in the filmis then subjected to color development in presence of a color developerand dye coupler and finally the silver is removed without affecting thestable and insoluble dye images that have been formed. The product willhave evenly colored areas of equal density, hue and saturation in theareas formerly occupied by the completely opaque silver. If the densityof the dye image is not believed sufficient, the image can beintensified by a repeat of the process.

The oxidation of the metallic silver can be by any of the oxidationagents known to be useful in the photographic art such as thosecontaining cupric ion, ferric ion or ferricyanide ion such as cuprichalides, e.g. cupric bromide chloride, cupric sulphate or nitrate,ferric chloride, bromide or sulphate, ammonium citrate or an alkalimetal ferricyanide such as sodium, potassium or ammonium ferricyanideand the like. Since dye is not present in the initial stage of theprocess, fairly vigorous oxidizing agents such as acidified potassiumbichromate, or potassium permanganate can be utilized. The latter twooxidizing agents are not preferred because of the tendency to stain orweaken the physical characteristics of the emulsion.

Since the purpose of the oxidation is to return the silver to areducible salt form, and not necessarily to a photosensitive form, it isnot essential that a halide be present in the bleach bath, thoughtypical commercial photographic bleaches are a combinationoxidation-rehalogenation type of compositions containing an alkali metalhalide such as a combination of potassium ferricyanide and potassiumbromide. Conversion of silver to a halide form is preferred since it iscompatible with the color developing compositions utilized in theprocess and formation of insoluble silver bromide propels the bleachingreaction to completion.

The color developer as previously discussed, is a combination of adeveloper and coupler portion. Because of instability of this developer,it is normally prepared within a short time before use by combiningseparate solutions of the developer and coupler. This solution usuallycontains additional ingredients such as an alkali to dissolve thecoupler and to activate the developer and a buffer to preservealkalinity. A small amount of sulphite acts as a preservative andbromide ion restrains development. Frequently an additional organicantifoggant such as benzotriazole is present. In some cases an organicsolvent is used instead of or in addition to alkali to dissolve thecoupler. Temperature during development should be kept constant, usuallyabout 68 F., and more uniform contrast is obtained in a shorter timewhen the bath is agitated.

The removal of the reduced silver and any residual halides remainingafter color development requires two operations: (1) fixing, theconversion of the silver into water soluble compounds such as halides,and (2) washing to remove these compounds. Although there are a numberof solvents for silver halides such as lithium or guanidine thiosulfate,potassium cyanide, thiourea, potassium or ammonium thiocyanate, onlysodium and ammonium thiosulfate are in widespread use. The life of thefixing bath is sometimes diminished by carry over of developingsolution. This may be prevented by use of a stop bath between developingand fixing or by addition of a developer stopping agent to the fixingbath.

The following is an example of a preferred procedure to be followed inthe rebleach process of color developing a previously developed blackand white high contrast film.

Example I (1) Softening of emulsion.The black and white developed andfixed film if dry is placed in water in a tray or under running waterfor about two minutes.

(2) Bleach of silver.-The film is then bleached from black to white inthe opaque areas represented by silver dots or lines by a bleach bathconsisting of equal amounts of potassium bromide and potassiumferricyanide dissolved in water. Within approximately one to twominutes, the silver is converted to silver bromide. Care is taken thatthe silver is completely bleached by inspection of both sides of thefilm.

(3) Wash film in running water for 15 seconds.

(4) Color development.Place film in color developing bath and agitateduring the first one to two minutes. Allow the film to completelyredevelop for approximately 57 minutes, inspecting the nonemulsion sideof the film to assure it is practically as dark as the original blackand white film. Developing time must be extended with developer that hasbeen mixed and used for over one hour. The composition of thisdeveloping bath will be described later.

(5) Rinse film in running water for approximately 15 seconds.

(6) Rebleach of film.Return film to bleach bath of step 2 forapproximately 15-40 seconds to again oxidize the silver to silverbromide. If the color intensity is not sufficient, steps 3-6 arerepeated at this time to intensify the color.

(7) Rinse film in running water for about 5 seconds.

(8) Fixing of film.Place film in fixing bath consisting of sodiumthiosulfate solution in water until all visible traces of residualsilver have been eliminated and a clear dye image remains. If residualtraces of silver remain after one minute, rinse and return to the bleachbath for a short time and rinse and refix.

(9) Rinse film in running water for one to three minutes.

(l) Drying of film.-Dry film in air and optionally with the use of mildheat.

The color developing solution is made in several parts as the keepingqualities are not good and activity decreases after the components arecombined. The first part of the color developing solution containssodium sulfite as an antioxidant, sodium carbonate as an alkali andpotassium bromide as a restrainer in the following proportions:

Working solution A:

Water (distilled)-32 oz. Sodium sulfite3 oz. Sodium carbonate3 oz.Potassium bromide-1 gram The second part contains a color developingportion, and two separate color forming solutions, a yellow color formerand a magenta color former.

Developer solution B:

Iisopropyl alcohol (70% v.)l.5 oz. 2 amino diethylaminotoluenemonohydrochloride1.75 g. Acetone-0.5 oz.

Magenta color former solution C:

P-nitrophenyl acetonitrile-0.4 g. Acetone-.1 oz.

Isopropyl alcohol (70% v.).1 02.

Yellow color former solution D:

Acetoacetanilide4.2 g. Isopropyl alcohol 70% v.)-1 oz. Acetone-1 oz.

The dry chemicals in Solutions B, C and D are dissolved in the firstorganic solvent with mixing and the second listed solvent is then added.The color former Solutions C and D are first mixed together withvigorous shaking and then are combined with Solution B. Six parts ofSolution A and 48 parts of water by volume are then combined with onepart of combined Solutions B, C and D. The mixture is mixed Well andaged 1-2 minutes before use.

An alternative procedure would be to bleach-rehalogenize according tosteps 1-3 and then color develop with developer solution and onecoupler, and then rebleachrehalogenize, color develop With the secondcoupler and complete the bleach-fix silver removal. This would doublethe amount of dye formed. The preferred color is obtained in either casewith a weight ratio of yellow to magenta of about 10 to 12 to 1.

The film of Example I is now a deep orange-red of the same hue,brightness and saturation in all the former black opaque silver areas. Aset of four color separation black and white high contrasttransparencies are processed according to the procedure of Example I todeep orange-red transparencies, and are registered, a

series of holes are punched into the perfectly registered set. Theseparation films are separated and three registered printing plates areprepared therefrom by placing them in contact to a presensitized diazoplate and exposure to a high intensity carbon arc at a distance of abouttwenty inches for 1-3 minutes. The plates when developed and worked upwith water and gum are completely unexposed in the correspondingred-orange areas of the film and print a perfectly registered image.

Two different fine screen half-tones are processed according to ExampleI and are registered on a stripping table by superimposing andoverlapping the dot patterns of a portion of the films. The registeredlayout when utilized to expose and develop a plate exhibits perfectregister and blending of the dot patterns on printing.

A surprint film with added shadow detail and the base image half-tonefilm are each processed according to Example I. The surprint issuperimposed and registered to the base film on a stripping table byobserving the transparent red-orange image of the base film. Thesurprint film is then taped to the base film and the ultraviolet opaquearea of the base film corresponding to the surprint is cut out. Theplate prepared from the assembled registered layout is perfect. Theplate could have been prepared from the base film alone and beforedeveloping the plate it could have been re-exposed to the surprint or tothe assembled registered combination to add the forgotten or laterdesired detail of the surprint.

With respect to the alternative process in which the latent silverhalide image areas of the exposed high contrast film are directly colordeveloped, it must be realized that the emulsion itself is slow speedand the aromatic diamine developer is a Weak developer. For this reason,the exposure is increased to approximately twice normal when thisprocess is utilized. With such an exposure to a half-tone or line image,the high contrast film can be developed according to the procedure ofExample I to a red-orange negative transparency of the samecharacteristics. The softening, bleaching and washing steps 1-3 are notnecessary in this procedure, and this process eliminates the necessityof prior black and white development. When a stronger caustic such assodium hydroxide is added to the color developer or substituted for atleast part or all of the sodium carbonate, the developing action is moreintensified and vigorous.

The process can be further simpliled by incorporating some of the colordeveloping ingredients directly into the emulsion. This avoids thestorage of some of the unstable chemicals and the requirement to mixthem immediately before use and discard after a short usage.Furthermore, with a direct color developing film the procedure can bestandardized and the technician will become educated and familiar withthe capabilities and the uses of a single, versatile material, ratherthan to have to work with separate materials that are processed indifferent manners with dilferent reagent solutions.

By reference to FIG. 2, it is observed that the film of the inventioncomprises a transparent support 3 on which is coated a photographicemulsion 4 containing an intimate dispersion of a color coupler andintimately dispersed, finely and evenly divided grains 5 of silverhalide. The transparent support may be polystyrene, a polyester such aspolyethylene terephthalate or a cellulose ester.

A coupler can be immobilized in the emulsion by the attachment of largeorganic groups to the basic coupler structure or the coupler can bedispersed throughout the emulsion in an oily, organic material. Thelarge organic group should not interfere with the color couplingcapacity of the coupler. A typical immobilized yellow coupler ism-stearoyl-aminobenzoylacetanilide p carboxylic acid and a typicalmagenta coupler is 1-(5'-sulfo- 3-stearoylaminophenyl)-pyrazolonesodium. The coupler solvent employed for dispersing a coupler in theemulsion is not especially critical and can be selected fromsubstantially water-insoluble low molecular weight organic crystalloidalmaterials having a boiling point above about 175 C. disclosed forexample in US. Pat. No. 2,322,027. There are other coupler solventsknown in the art. Suitable specific solvents are the lower dialkylphthalates such as dibutyl phthalate.

The following is a typical procedure for forming a non-relieved i.e.planographic, single emulsion, monochromatic, transparent film of theinvention capable on color development of transmitting radiation otherthan radiation of wavelengths of from 300 to 500 millicicrons, andespecially of from 350 to 450 millicrons. To a high contrast gelatinemulsion containing a dispersion of substantially even grain silverhalide of less than about 0.3 micron average diameter, is added adispersion of a water immiscible organic solvent solution of at leastone coupler capable of color development in the presence of silverhalide to an ultraviolet absorbing, but otherwise transparent dye image.The high contrast emulsions contain from 40 mol percent chloride and 60mol percent bromide to 90 mol percent chloride and 10 mol percentbromide. The emulsion can also contain small amounts of from 1 to 2 molpercent silver iodide. Alternatively, the color coupler can be in theform of a layer adjacent the silver halide emulsion layer.

The following is a disclosure of an embodiment of the novel film of theinvention.

Example H A high contrast 0.1 micron average fine and even grain silverchloro-bromide emulsion in gelatin is prepared according to theprocedure of the examples of U.S. Pat. No. 2,756,148. A molar equivalentamount with respect to silver of the color couplers of Example I of thisdisclosure in dibutyl phthalate is intimately dispersed throughout theemulsion. The emulsion is coated on a transparent support and when dryis exposed to a transparency at double the normal exposure for the corresponding black and white high contrast film. The exposed film is thenprocessed With a mixture of Solutions A and B of Example I diluted withthe proper amount of water, and developed for 4 to 6 minutes. The filmis then processed according to steps 4-10 of Example I to yield ared-orange transparent film of even density saturation and hue which isof the same quality as the high contrast films made by Example I or thedirect color development procedure of the present disclosure.

Again, in this procedure, the stain of the background can be reduced andthe development power of the developer boosted by substituting sodiumhydroxide for at least part of the sodium carbonate. The exposed filmmay be subjected to non-color developing black and white high contrastdevelopment before color development. In the latter case, the emulsionis fixed and bleached before color development and the exposure time canbe the normal exposure for the corresponding black and white highcontrast film of equal characteristics. An anti-halation layer behindthe emulsion and an outer anti-abrasion layer may be provided accordingto procedures well known in the art.

In the exposure and processing of deep-etch type of photomechanicalsensitized reproduction plates such as the S series of the 3M Company,the plate is exposed to a positive rather than a negative high contrastfilm. In making this positive according to prior procedures, it isnecessary to expose the original copy to a sheet of film in the camera,develop the film to a negative. A positive is then prepared by placingthe negative in contact with another sheet of film, exposing through thebase of the negative to effect lateral reversal and then developing thepositive. The negative could be exposed through the base to obtainlateral reversal, developed and then placed in contact with anothersheet of film, emulsion to emulsion, exposed and developed to obtain acorrectly reading positive. In the lateral reversal technique a slightdegree of sharpness of 12 the overall printing positive is lost unlessan additional generation of reversal is carried out.

The present invention includes within its scope a method of preparingsuch positives in which a generation of photographic processing iseliminated, thus making for a more convenient procedure and furtherassuring a higher resolution, quality product. In such a process directreversal of camera speed film during processing reverses the negativelatent image of an exposed high contrast film to an orange-red highcontrast positive eliminating at least one generation of reproductionprocessing.

In one procedure the color coupler containing single emulsion film ofExample II is exposed to a half-tone positive and the negativelight-sensitized areas are developed in a non-color developing black andwhite high contrast developer until development is complete and theaction of the developer is then terminated by means of an acid shortstop bath. The black and white developed film is then completely exposedto white light which activates the remaining light sensitivenon-developed silver halide grains and these grains are then colordeveloped and all the silver is fixed and removed according to themethod of Example II. A reversed red-organge half-tone transparencyresults which is identical in properties to the films produced by theother procedures of the invention.

A reversed film can also be prepared with a black and white highcontrast film by exposure of the film to a positive. The exposed film isprocessed by non-color developing, acid-fixing, re-exposure of thecomplete film and then color developing and removing all the silver byfixing according to steps 4-10 of Example I.

It is to be understood that the foregoing only relates to preferredembodiments of the invention, and that numerous modifications oralterations are possible without departing from the spirit and scope ofthe invention as set forth in the appended claims.

What is claimed is:

1. The process for preparing a photomechanical plate comprising thesteps of: 7

developing with a color coupling dye the silver bearing image areas ofan exposed high contrast photographic emulsion to form a color coupleddye associated with the reduced silver;

removing the silver from said emulsion without affecting said dye toform a photographic transparency consisting of clear areas and dyecolored areas, the dye colored areas being substantially transparent tovisible radiation and substantially opaque to ultraviolet radiation;

placing a plurality of said transparencies in proper registry bysuperimposing said transparencies, simultaneously viewing the images ofsaid transparencies by visible light and positioning said transparenciesin proper relationship;

exposing an ultraviolet sensitive plate through said transparenciesindividually to a source of sensitizing radiation, said transparenciesbeing placed in rela tive registry during exposure of said plate,whereby the images on said plate are exposed in proper relationship.

2. The process as defined in claim 1 wherein the dye colored areas are apronounced red-orange of even hue and saturation allowing substantialtransmission of radiation of a wavelength above 500 millimicrons, and ofa minimum brightness or density to prevent transmission of more thanabout 10 percent of radiation within the range of 350 milli-microns to450 millimicrons.

3. The process as defined in claim 1 comprising the additional step ofintensifying the dye image by repeatedly bleaching and color developingsaid image before removing the silver salt from the emulsion.

4. A method of forming an image on a mechanical reproduction platesensitive to radiation in the range of 13 from 300 millimicrons to 500millimicrons, comprising the steps of:

superimposing a plurality of high contrast photographic films in whichthe radiation absorbing areas are silver free and contain a dye whichhas a substantial transmission above said radiation range and less than20 percent transmission within said range;

viewing through said plurality of films by means of a source ofradiation having substantial emission above said radiation range;

aligning while viewing through said plurality of films to establish thedye patterns in an exact registered relationship;

providing mechanical means for reestablishing said registry between saidfilms; and

interposing said films individually in relative registry between saidplate and a source of radiation having substantial emission in the givenrange, thereby exposing said plate to a plurality of registered images.

5. The method as defined in claim 4 wherein two of said films comprisedifierent half-tone image bearing films; said films are overlapped, thedot patterns placed in registry by viewing under illumination thedistinct and pronounced colored, partially transparent, dots; the filmsare attached together before exposing the plate; and the attached filmsare exposed as an individual film.

6. A method of forming and using a high contrast film containingpronounced red-orange colored, finite and distinct dyed areas of evenhue and saturation allowing substantial transmission of radiation of awavelength above 500 millimicrons, each dyed area being of a minimumbrightness or density to prevent transmission of more than about 10percent of radiation within the range of 350 millimicrons to 450millimicrons, comprising the steps of:

converting the black opaque silver areas of an exposed, developed andfixed high contrast photographic filmhaving a maximum gamma of 4 to 5and an angular slope of 75-85 degrees of the sensitometric curve to areduced silver halide by a bleaching-rehalogenation of said film;

developing the finite silver bromide image areas by means of a yellowcolor coupler and a magenta color former to form pronounced red-orangeimage areas in association with reduced silver;

rebleaching and rehalogenating the silver;

converting said silver to a water soluble salt;

removing the water soluble silver salt from the emulsion leavingred-orange image dye areas which allow substantial transmission ofradiation of a wavelength above 500 millimicrons and preventtransmission of more than about percent of radiation Within the range of350 millimicrons to 450 millimicrons;

superimposing a plurality of said films;

viewing said films by means of a source of radiation having substantialemission of a Wavelength above 500 millimicrons;

aligning while viewing through said plurality of films to establish thedye patterns in exact registered relationship;

providing mechanical means for reestablishing said registry between saidfilms; and

interposing said films individually in mechanically fixed relativeregistry between a mechanical reproduction plate which is sensitive toradiation in the range of 350 millimicrons to 450 millimicrons and asource of radiation having substantial emissions in said range forthereby exposing said plate to form a plurality of images which are inregistry on the exposed plate.

7. A method of forming and using a high contrast reversal filmcontaining pronounced red-orange colored, finite and distinct dyed areasof even hue and saturation allowing substantial transmission ofradiation of a wavelength above 500 millimicrons, each dyed area beingof a minimum brightness or density to prevent transmission of more than'about110 percent of radiation within the range of 350 millimicrons to450 millimicrons, comprising the steps of:

1, developing an exposed high contrast black on white film'to form animage of reduced silver; exposing the developed film to white light toform a latent reversal image; developing the reversal image areas bymeans of a yellow color coupler and a magenta color former to formpronounced red-orange reversal image areas in association with reducedsilver;

bleaching the reduced silver image;

converting the silver to a water soluble salt;

removing the water soluble silver salt from the emulsion leavingred-orange reversal image dye areas which allow substantial transmissionof radiation of I a wavelength above 500 millimicrons and preventtransmission of more than about 10 percent of radiation within the rangeof 350 millimicrons to 450 millimicrons; superimposing a plurality offilms having image areas which have said transmission characteristics;viewing said films by means of a source of radiation having substantialemission of a wavelength above 500 millimicrons; aligning while viewingthrough said plurality of films to establish the dye patterns in exactregistered relationship;

providing mechanical means for reestablishing said registry between saidfilms; and

in'terposing said films individually in mechanically fixed relativeregistry between a mechanical reproduction plate which is sensitive toradiation in the range of 350 millimicrons to 450 millimicrons and asource of radiation having substantial emissions in said range forthereby exposing said plate to form a plurality of images which are inregistry on the exposed plate. 8. A method according to claim 1, inwhich the silver in metal form is oxidized and color-developed by acolorcoupling reducing developer and the silver is dissolved and removedby bleaching and fixing.

9. A method according to claim 1, in which latent image areas of anexposed silver halide containing high contrast emulsion are directlycolor-developed.

10. A method according to claim 1, in which the silver halide emulsioncontains one of the color forming reactants.

References Cited UNITED STATES PATENTS 2,312,875 3/1943 Bunting et al.96-54 2,884,325 4/ 1959 Burgardl et al. 96-54 3,291,603 12/1966 Bryan96-73 OTHER REFERENCES E. latte, E. Brody, F. Preucil, J. White, Color.Separation Photography, For Offset Lithography, Lithographic TechnicalFoundation, Inc., 131 E. 38th St, New York, N.Y., 1959, PP. 30-32.

NORMAN G. TORCHIN, Primary Examiner J. E. CALLAGHAN, Assistant ExaminerU.S. Cl. X.R. 9631

